The present invention relates to an extruder used in a plastic extrusion process.
A conventional extruder used in a plastic extrusion process is one which comprises an elongated auger which operates in stages lengthwise of the extruder. These stages comprise an initial feeding of the plastic at the upstream end of the extruder, then a transition of the plastic from a solid to a more flowing state, and finally a metering of the plastic at the downstream end of the extruder. This type of extruder, while being very efficient in operation, takes up substantial floor space as a result of its extended length required in performing all of the above operation stages.
Another type of extruder taking up very little floor space, but which has been used to a very limited extent, is one which comprises a rotating disk. This type of extruder has not been overly successful due to excessive pressure build up on the disk which occurs as a result of all three of the above operation stages, i.e. feed, transition and metering occurring across the diameter of the disc.
The present invention provides an extruder which is used in a plastic extrusion process having the small space requirement benefits of the above mentioned disk type extruder but without suffering from the pressure related problems of known disk type extruders. More specifically, the extruder of the present invention, which is supplied with plastic material to make product from the plastic material comprises a plurality of extruder members each of which comprises a plate portion and a hollow tubular portion which is perpendicular or at least substantially perpendicular to the plate portion. The plate portions of the extruder members are located side by side with one another defining a first plastic handling part of the extruder and the tubular portions of the extruder members are telescopically interfitted with one another to define a second plastic handling part of the extruder.
In accordance with the present invention, feed and transition of plastic material introduced to the extruder is carried out in the first plastic handling part of the extruder and the metering of the plastic flow from the extruder is carried out in the second plastic handling part of the extruder. This separation of the metering from feeding stage of operation of the extruder eliminates the pressure related problems of known disk type extruders. At the same time, the extruder of the present invention does not require the large amount of floor space used by lengthy auger type extruders.